1. Field of the Invention
The present invention relates to a polymerizable composition and a planographic printing plate precursor, an alkali-soluble polyurethane resin, as well as a process for producing a diol. More particularly, it relates to a polymerizable composition suitable for a photosensitive layer of a negative planographic printing plate precursor in which writing at a high sensitivity with laser light is possible, a negative planographic printing plate precursor including the polymerizable composition in a photosensitive layer, an alkali-soluble polyurethane resin excellent in solubility in an aqueous alkali solution contained in the polymerizable composition, and a process for producing a diol compound suitable as a raw material of the polyurethane resin.
2. Description of the Related Art
Conventionally, as a photosensitive planographic plate printing precursor, a presensitized plate in which a lipophilic photosensitive resin layer is provided on a hydrophilic support has been widely used. As the process for manufacturing the plate, a desired printing plate has been obtained by dissolving and removing a non-exposed part after mask exposure (surface exposure) via a lithographic film.
In recent years, a digitalization technique has come into wide use, in which image information is electronically treated, accumulated and outputted using a computer. Further, a new image outputting format responding to such a digitalization technique has been put into practice in various ways. As a result, a computer to plate (CTP) technique of scanning light having high directivity such as laser light according to digitalized image information, and directly manufacturing a printing plate without using a lithographic film has received attention, and an important technical issue concerns how to obtain a planographic printing plate precursor adapted thereto.
As such a planographic printing plate precursor which can be scanning-exposed, a configuration in which a lipophilic photosensitive resin layer (hereinafter, also referred to as photosensitive layer) containing a photosensitive compound which can generate an active species such as a radical or Bronsted acid by laser exposure is provided on a hydrophilic support has been proposed, and is already commercially available. By laser exposure-scanning this planographic printing plate precursor based on digital information to generate an active species only in a laser-irradiated region, and by insolubilizing the region by causing a physical or chemical change in the photosensitive layer as a result of the irradiation, followed by developing treatment, a negative planographic printing plate can be obtained. In particular, a planographic printing plate on which a photopolymerizable photosensitive layer including a photopolymerization initiator excellent in photosensitive speed, a compound containing a polymerizable ethylenic unsaturated double bond and a binder polymer soluble in an alkali developer and, further, optionally, an oxygen impermeable protective layer, are provided, can provide a printing plate having a desirable printing performance due to advantages such as excellent productivity, simplified developing treatment, and favorable resolution and ink receptivity.
A polymerizable composition forming a photosensitive layer of such a planographic printing plate precursor is required to have properties such that an energy-imparted region is rapidly cured to form a film having a high strength and, at the same time, an unexposed part is rapidly dissolved and removed by an alkali developer.
Conventionally, for the purpose of improving a cured film strength, and imparting an image region in the planographic printing plate with high printing durability, a polyurethane resin binder comprising an alkali-soluble group has been used in such a photosensitive polymerizable composition (see, for example, Japanese Patent Application Publication (JP-B) No. 8-12424 and Japanese Patent Application Laid-Open (JP-A) No. 1-271741). As the alkali-soluble group contained in such a polyurethane resin binder, dimethylolpropionic acid and dimethylolbutanoic acid are generally used. However, the polyurethane resin binder may not be sufficient in developability due to high aggregating property arising from a urethane bond part and, in a developing layer, development scum is precipitated over time, and adhered to a plate material after plate making to generate stains and, therefore, there is a problem that it is difficult to obtain excellent image forming property when used in the photosensitive layer in the planographic printing plate precursor.
In response to such a problem, for example, a technique of using a carboxylic acid unit having a specified structure in a urethane resin for the purpose of improving alkali developability, and a technique of introducing a unit into a urethane resin for the purpose of assisting developer solubility by a method of using a compound producing an acid group by hydrolysis as a raw material have been proposed (see, for example, JP-A No. 2006-225432). In a polymerizable composition containing a urethane resin obtained by such a method, alkali developability is improved, and precipitation over time of development scum in a developer is effectively suppressed. However, improvement in solubility in an alkali developer influences the excellent film property originally possessed by a polyurethane resin, whereby the film property of the resulting film is degraded, and a problem may arise whereby, when used in the photosensitive layer of the planographic printing plate precursor, printing durability is deteriorated.
In this way, in the polymerizable composition, the strength of a cured film, and developability of an uncured region generally have incompatible properties and, in particular, when used as the photosensitive layer of the planographic printing plate precursor, these properties lower the printing durability of an image part and increase contamination of a non-image part and, therefore, a polymerizable composition which resolve both of these issues is currently necessary.